In a known technology for producing semiconductors, a process of ion implanting various types of conductive impurities, such as boron (B), phosphorus (P), and arsenic (As), as a solid gas onto a surface of a semiconductor substrate is extensively used. In a beam line type ion implanter that is used in the ion implanting process, in order to prevent splitting of charges of the device on a wafer or in order to prevent divergence of beam resulting from the space charge effect of the ion beam, a charge neutralizing device that reduces accumulation of the charge by supplying electrons having low energy to beam plasma or a surface of the wafer is frequently used.
FIG. 10 schematically illustrates a mechanical scan type ion implanting device, which is called a high current ion implanter. The ion implanting device 1 is mainly formed of three parts, that is, an ion source chamber 2, a beam line 3, and an end station part 4. The ion source chamber 2 includes an ion source 5 that generates high density plasma using an arc discharge and extraction electrodes 6 that electrostatically extracts ions to accelerate the ions. The beam line 3 includes a magnetic deflection type mass separator 8 that selects desired dopant ions from the ion beam 7 emitted from the ion source chamber 2, and a trimming aperture 9 for shaping the ion beam 7 or a mass resolving slit 10 that is provided on the focus of the analysis magnet to select the desired dopant ions. The end station part 4 includes a Faraday cage 11 and a beam catcher 12 for measuring a beam current, a rotating disk 14 on which a semiconductor substrate 13 is mounted and which scans the substrate so that the ion beam 7 is uniformly applied to the substrate, and an electron gun 15 that acts as the charge neutralizing device.
The implantation of the ions is performed using the above-mentioned ion implanting device through the following procedure. First, high density plasma is generated using the dopant gas or solid vapor required in the ion source 5. Subsequently, desired acceleration energy is provided at the same time the ions are extracted using the extraction electrodes 6. The accelerated ion beam 7 is selected as the desired dopant ion using the mass separator 8, shaped using the trimming aperture 9 or the mass resolving slit 10, and induced to the object. Meanwhile, the substrate 13 is transferred to the rotating disk 14 and then mounted at a predetermined position. Typically, a plurality of substrates 13 is mounted.
Next, the rotating disk 14 that is provided at a start position (A) that rotates a predetermined number of times, as shown in the drawing and, at the same time, translation (B) is performed. This process is called the mechanical scan type. In the process, the ions are implanted on the entire surface of each substrate of the plurality of substrates 13. The translation is repeated several times to improve implantation uniformity.
Generally, before the ions are implanted, a pattern of a gate electrode is formed on the substrate 13. FIG. 11 illustrates an example of the patterned gate electrode. In this drawing, the substrate 23 (13) is, for example, a P-type substrate, a thick field insulating film 20 is formed on the main surface portion of the substrate 13, a thin insulating film 21 acting as a gate insulating film is formed on a portion of an active region between the insulating films 20, and a gate electrode 22 is formed on the thin oxide film 21. In this state, ion implantation is performed to form impurity regions acting as a source and a drain on the substrate 13 that are provided at both sides of the gate electrode 22. In this case, the ion beam 7 may be formed of phosphorus or arsenic in order to form the N-type source and drain.
When the ions are implanted on the insulating film as described above, particularly, in the case of when the ions are implanted using a beam current of 1 mA or more, the possibility of cracks occurring to the gate insulating film 21 may be increased. To prevent the cracking, a charge neutralizing device shown in FIG. 12 is used in the related art. The charge neutralizing device accelerates first electrons emitted from the electron gun 15 using an electric field of 300 V to radiate the first electrons onto the corresponding Faraday cage 11, thus generating second electrons 23. A portion of the second electrons 23 is provided to the substrate 13 to neutralize the positive charge accumulated on the gate electrode 22. Thereby, the cracking of the gate insulating film 21 may be prevented.
As described above, in the known charge neutralizing device, an electron source or a plasma source is provided so that the electron source or the plasma source approaches the beam at the middle point of the beam line and an electronic current emitted therefrom overlaps the beam and plasma.
However, in the above-mentioned technology, even though charge neutralization occurs at a point close to the electron source, the charge neutralization may not occur at the opposite point (the point that is furthest from the electron source), causing charges of the device to split or divergence of the beam.
Additionally, in a beam-scanning type an ion implanter, the coupling efficiency of supplied electronic current and beam plasma is poor, thus it is very difficult to perform high current ion implantation using the known charge neutralizing device.
Further, in the ion implanter, as described above, the positive charges that are accumulated on the gate electrode 22 are neutralized by the second electrons 23 that are generated from the surface of the Faraday cage 11 due to radiation of the first electrons emitted from the electron gun 15. However, a portion of the first electrons approaches the substrate 13 due to reflection. Accordingly, there is a problem in that high-speed electrons having energy of 300 eV charge the substrate 13 such that the substrate has a negative charge. Furthermore, cracking occurs due to the negative charge, and the gate insulating film 22 deteriorates even if the cracking does not occur.
FIGS. 13 and 14 illustrate a charge neutralizing device where a magnetic dipole type plasma generator for providing electrons having energy of 50 eV or less that includes an extraction electrode for extracting electrons from plasma and a deceleration electrode for decelerating the electrons extracted using the extraction electrode is provided on a front surface of a substrate to be treated (Patent Document 1). In this document, since the magnetic dipole type plasma generator is used as an electron source and a cusp magnetic field where a magnetic field is not present in the plasma is formed in the magnetic dipole type plasma generator, it is possible to easily extract high density plasma of several eV having a predetermined electronic temperature by only applying the magnetic field. The electrons having low energy are supplied to a front surface of the semiconductor substrate that is an object to form the electronic clouds. Therefore, the electrons are supplied to only a portion of the semiconductor substrate that is positively charged, thereby performing charge neutralization. Accordingly, it is possible to perform desired charge neutralization even though charge depends on an ion implantation condition or a device condition. Furthermore, it is possible to form uniform electronic clouds having a large area by using the magnetic dipole type plasma generator.
Patent Document 1: JP-B-8-21361